I run a 275/50/15 ET Street Radial on the back of my Prostars. I actually like the way my 275/60/15s look better, that are on my Magnum 500s, and i originally had that size M/Ts on my Prostars too, but the car was a little underpowered with the old combo, so when it dead hooked, it fell flat on its face. I switched to the shorter tire, and it helped my short times a bunch.
I can't remember what size tire is on the front. I'll have to look. They're Hoosier front runners.